Translating fan blades for an aircraft tail mounted fan assembly

Abstract

The present disclosure is directed to a fan section mounted to an aircraft tail section. The fan section defines a radial direction, an axial direction and a circumferential direction. The fan section includes a shaft extending generally along a longitudinal axis, and a plurality of fan blades rotatable with the shaft about the longitudinal axis. Each fan blade defines an outer end along the radial direction. One or more of the plurality of fan blades translates a respective outer end from a first radial position to a second radial position.

What is claimed is: 
     
       1. A single stage fan section mounted to an aircraft tail section, the fan section defining a radial direction, an axial direction and a circumferential direction, the fan section comprising:
 a shaft with a hub extending generally along a longitudinal axis; and 
 a single stage fan comprising a plurality of fan blades rotatable with the shaft about the longitudinal axis, wherein each fan blade defines an outer end along the radial direction; 
 wherein one or more of the plurality of fan blades translates a respective outer end along the radial direction from a first radial position to a second radial position; and 
 wherein the first radial position is an extended position and the second radial position is a retracted position, the second radial position being approximately equal to an outer diameter of the hub. 
 
     
     
       2. The fan section of  claim 1 ,
 wherein the hub comprises a sheath, wherein the sheath is disposed at least partially within the hub along the radial direction, and wherein the sheath translates one or more of the plurality of fan blades inward and outward of the sheath along the radial direction. 
 
     
     
       3. The fan section of  claim 2 , wherein the sheath is coupled to the shaft. 
     
     
       4. The fan section of  claim 1 , wherein each fan blade comprises at least one nested portion arranged along the radial direction, wherein the at least one nested portion translates inward and outward along the radial direction. 
     
     
       5. The fan section of  claim 1 , wherein the plurality of fan blades translates inwardly along the radial direction to a position representing at least a 25% decrease in the first radial position. 
     
     
       6. The fan section of  claim 1 , wherein one or more of the plurality of fan blades translates a respective outer end from the first radial position to the second radial position during a takeoff operating mode. 
     
     
       7. The fan section of  claim 1 , wherein the plurality of fan blades comprises at least three fan blades. 
     
     
       8. The fan section of  claim 1 , the fan section further comprising:
 a locking mechanism, wherein the locking mechanism positions the fan blades in a stationary position along the circumferential direction. 
 
     
     
       9. The fan section of  claim 1 , wherein each of the plurality of fan blades defines a pitch axis, and wherein the plurality of fan blades are each rotatable about their respective pitch axis. 
     
     
       10. The fan section of  claim 1 , wherein the fan section is a boundary layer ingestion fan section for ingesting and energizing a boundary layer airflow over the aircraft tail section. 
     
     
       11. The fan section of  claim 1 , wherein less than all of the plurality of fan blades translates its respective outer end from the first radial position to the second radial position. 
     
     
       12. The fan section of  claim 1 , wherein at least one of the plurality of fan blades is a radially stationary fan blade. 
     
     
       13. The fan section of  claim 1 , wherein one or more of the plurality of fan blades is configured to be in the second radial position inward of the first radial position during a takeoff operating mode, and is configured to be moved from the second radial position to the first radial position after the takeoff operating mode. 
     
     
       14. The fan section of  claim 1 , wherein moving one or more of the plurality of fan blades from the first radial position to the second radial position increases a ground clearance of the aircraft tail section. 
     
     
       15. A single stage fan section mounted to an aircraft tail section, the fan section defining a radial direction, an axial direction and a circumferential direction, the fan section comprising:
 a shaft extending generally along a longitudinal axis; and 
 a single stage fan comprising a plurality of fan blades rotatable with the shaft about the longitudinal axis, wherein each fan blade defines an outer end along the radial direction; 
 wherein one or more of the plurality of fan blades translates a respective outer end along the radial direction from a first radial position to a second radial position, the first radial position being an extended position and the second radial position being a retracted position; 
 
       wherein each fan blade comprises at least two nested portions; and 
       wherein the at least two nested portions translate inward and outward from one another along the radial direction. 
     
     
       16. The fan section of  claim 15 , wherein the fan section is a variable pitch fan. 
     
     
       17. A fan section mounted to an aircraft tail section, the fan section defining a radial direction, an axial direction and a circumferential direction, the fan section comprising:
 a shaft with a hub extending generally along a longitudinal axis; and 
 a plurality of fan blades rotatable about the longitudinal axis, wherein each fan blade defines an outer end along the radial direction, and wherein one or more of the plurality of fan blades translates a respective outer end from a first radial position to a second radial position, the second radial position being approximately equal to an outer diameter of the hub; 
 wherein the fan section is a boundary layer ingestion fan section for ingesting and energizing a boundary layer airflow over the aircraft tail section; and 
 wherein moving one or more of the plurality of fan blades from the first radial position to the second radial position increases a ground clearance of the aircraft tail section. 
 
     
     
       18. The fan section of  claim 17 , wherein the plurality of fan blades comprises a first plurality of fan blades and a second plurality of fan blades, wherein the first plurality of fan blades are spaced from the second plurality of fan blades along the longitudinal axis, wherein the first and second plurality of fan blades are in contrarotating arrangement.